As one of the first commercially available synthetic thermoplastic polymers, polyamide resins have found widespread use in many applications. Polyamides, which include aramids, are commonly used in fabrics, pipes, and ballistic fibers. Polyamides include those sold under the brand names Rilsan® and Hiprolon® by Arkema, Inc.
In one application, polyamides are used make natural gas pipes for natural gas distribution and use. Pipes made with polyamides may have pressure limitations, identified as pressure ratings, when used as natural gas pipe. Higher internal pressures can deform, e.g., expand, and change diameter of the pipe, often to deleterious effect. This deformation is typically referred to as “creep” of the polymer. Increased creep resistance may be associated with an excessive increase in viscosity of the molten polyamide. Excessively higher viscosities are undesirable because they can make extruding polyamide articles more difficult and/or commercially impractical. In addition, through continued use such polyamide gas pipe may deform by increasing in diameter due to the pressure of the natural gas.
When molding polyamides, polyamide typically is dried to remove any water prior to melting and processing to prevent hydrolysis, which can result in chain scission and degradation, as well as loss of physical properties such as strength. Drying the polyamide increases cost in both time and energy.
Further information is described in U.S. publication No. 20120142887, U.S. publication No. 201001081073, U.S. publication No. 20040118468, U.S. publication No. 20060185750, U.S. Pat. No. 7,915,336, U.S. Pat. No. 6,863,981, U.S. Pat. No. 5,270,377, and U.S. Pat. No. 4,619,962.
Therefore, it is desirable to increase the strength of the polyamide to provide greater creep resistance, while still having good viscosity under extrusion conditions. A polyamide having greater creep resistance while maintaining an acceptable viscosity for extrusion can allow polyamide articles to be made via extrusion processes known in the art such as pipe, profiles, fibers, sheet, film and non-woven applications. This also applies to injection molding, compression molding, thermoforming, transfer molding and rotational molding operations.
It is desirable to develop methods of processing polyamides that can be performed without the added step of drying the polyamide before processing while avoiding hydrolysis of the polyamide or weakening of the polyamide article.